Tower building games are known in which a number of rectangular bricks are arranged in layers to form a tower, with the orientation of the rectangular bricks alternating from one layer to the next to provide frictional coupling between layers and adjacent bricks in the same layer. During a typical play scenario, the height of the tower is increased by removing bricks from one or more lower layers to build successive upper layers. A brick is a key brick if it is directly under the center of gravity of the bricks above it and is (or will be) the only brick in a given layer, or if it is one of two remaining bricks on either side of the center of gravity of the bricks above it. The game ends if the tower collapses because a key brick has been removed, or if the tower becomes unstable or is knocked over during the attempted removal of any brick. Since there may be slight variations in the thickness of the individual bricks or the tower may not be exactly vertical, the weight of the upper layers may not be evenly distributed on all bricks of a given layer. Accordingly, even a brick which is not a key brick may be supporting much of the weight of the tower in which case one or more bricks in adjacent layers will be dragged out of position by friction when the weight-supporting brick is removed. Thus, it is conventional to permit players to test for loose bricks before deciding which brick to remove, but to restrict players to the use of a single hand while removing bricks. An example of such a game using precisely manufactured polished wooden bricks is sold under the trademark JENGA by the Milton Bradley Company.
A known variant marketed in Canada under the trademark JENGA ULTIMATE utilizes more than one color of rectangular brick, with the different colors randomly distributed throughout the original tower. A die is rolled to determine what color brick must be removed during the next round of play, thereby adding an element of chance to the game's outcome.
Although the described games use bricks having length to width ratio of about 3:1, whereby three bricks may be initially arranged in a compact square layer having three contiguous bricks, similar tower building games are known in which somewhat narrower rectangular blocks are initially spaced apart horizontally. Other known variants use plastic rectangular bricks.